Stroma is the ground matrix of:

Explanation

The correct answer is chloroplast. The stroma is the ground matrix of a chloroplast, which is crucial for the photosynthesis process. It is the site for the Calvin cycle, where carbon fixation takes place. The other options are incorrect: Lysosomes are involved in waste processing, ribosomes are involved in protein synthesis, and 'oxysomes' is not a recognized term in cellular biology.